• Energy Research

Biogas plants can contribute to future energy systems’ stability through flexible power generation. To provide power flexibly, a demand-oriented biogas supply is necessary, which may be ensured by applying flexible feeding strategies. In this study, the impacts of applying three different feeding strategies (1x, 3x and 9x feeding per day) on the biogas and methane production and process stability parameters were determined for a biogas plant with a focus on waste treatment. Two feedstocks that differed in (1) high fat and (2) higher carbohydrate content were investigated during semi-continuous fermentation tests. Measurements of the short chain fatty acids concentration, pH value, TVA/TIC ratio and total ammonium and ammonia content along with a molecular biology analysis were conducted to assess the effects on process stability. The results show that flexible biogas production can be obtained without negative impacts on the process performance and that production peaks in biogas and methane can be significantly shifted to another time by changing feeding intervals. Implementing the fermentation tests’ results into a biogas plant simulation model and an assessment of power generation scenarios focusing on peak-time power generation revealed a considerable reduction potential for the needed biogas storage capacity of up to 73.7%.

Ethanol produced from renewable resources is widely regarded as an option to substitute traditional fossil fuels. By coupling the ethanol production to biogas production, an energy autarkic process with minimum ecological footprint can be created. Capable engineering tools are needed to design such processes due to their complexity and the integration necessary. Here, we present a modeling strategy that can serve this task as it allows the steady-state flowsheet simulation of biotechnological production of alternative fuels from renewable resources. The modeling concept is explained and applied to a small-scale self-sustaining ethanol production (1,000 t/a fuel-grade ethanol). An adjunct pinch-analysis for heat integration further demonstrates the potential of the tool developed for the investigation and design of future production of fuel and chemical raw materials.

Cannabinoids have gained significant interest as they may have pharmaceutical and nutritional applications to treat various diseases (sclerosis, glaucoma, and epilepsy, among others). Hemp (Cannabis sativa L.) has been studied recently as a source of cannabinoids, given the low concentration of tetrahydrocannabinol and comparatively high concentration of cannabidiol. Most of the plant’s fractions are used (blossoms, stem, and seeds), but the processing of the blossom leaves a residue, threshing residues, which could still be used to extract cannabinoids, aiming for an integral usage of the plant. Different technologies have been applied for cannabinoid extraction. Among these, pressurized liquid extraction (PLE) stands out due to the ease of application and efficiency. This work evaluates the influence of temperature, pressure, extraction time, and the number of cycles for the PLE of cannabinoids from hemp threshing residues using ethanol. Results show that low pressures, 100 °C, and 60 min are sufficient to achieve extraction yields of 19.8 mg of cannabidiol per g of dry hemp, which corresponds to an extraction efficiency of 99.3%. These results show this technology’s potential for cannabinoid extraction (mainly cannabidiol) and further open the perspective to valorize the residues and other parts of hemp plants.

This present work shows that the joint application of process simulation and computational fluid dynamics (CFD) is a helpful tool for the design and optimisation of complex and innovative concepts in chemical engineering practice. The application of these tools to the presented concept of a baled biomass-fired combustion chamber enables the optimisation of operation parameters such as the flue gas recirculation rate and excess air supply. Moreover numerous variations of the detailed engineering of the involved apparatuses can be simulated before realisation. The major goals comprise the maximisation of the thermal efficiency and the reduction of gaseous and particulate matter emissions. To meet these goals it is rather important to have available validated mathematical models with sharpened model parameters. Therefore the presented model approaches have been validated and refined using results from extensive combustion experiments conducted at an existing 2 MW pilot plant. Several modelling approaches are presented that especially focus on the treatment of the heterogeneous combustion and prediction of gaseous emissions such as carbon monoxide and nitrogen oxide. With validated models on a sound physical basis, process simulation and computational fluid dynamics enable a significant reduction of the development costs and the time-to-market of innovative chemical engineering concepts.

The full utilization of renewable raw materials is necessary for a sustainable economy. Lignin is an abundant biopolymer, but is currently mainly used for energy production. Ethanol organosolv pre-treatment produces high-quality lignin, but still faces substantial economic challenges. Lignin solubility increases with temperature, and previous studies have shown that it reprecipitates during cooling after the pre-treatment. Thus, a possibility for the optimization of lignin production with this process can be the separation of extract and residual biomass at high temperatures. In this work, lignin was extracted from wheat straw at 180 °C, and the extract was separated from the remaining solids at several temperatures after the pre-treatment. The results show that 10.1 g/kg of lignin and 2.2 g/kg of carbohydrates are dissolved at the pre-treatment temperature of 180 °C, which is reduced to 8.6 g/kg of lignin and 1.2 g/kg of carbohydrates after cooling. The precipitation of lignin separated from the extracts at 180 °C showed that a higher lignin concentration at high temperatures results in a 46% improvement in the yield of solid lignin, while there was no significant impact on the lignin purity.

Agrarian biomass as a renewable energy source can contribute to a considerable CO(2) reduction. The overriding goal of the European Union is to cut energy consumption related greenhouse gas emission in the EU by 20% until the year 2020. This publication aims at optimising the methane production from steam-exploded wheat straw and presents a theoretical estimation of the ethanol and methane potential of straw. For this purpose, wheat straw was pretreated by steam explosion using different time/temperature combinations. Specific methane yields were analyzed according to VDI 4630. Pretreatment of wheat straw by steam explosion significantly increased the methane yield from anaerobic digestion by up to 20% or a maximum of 331 l(N)kg(-1) VS compared to untreated wheat straw. Furthermore, the residual anaerobic digestion potential of methane after ethanol fermentation was determined by enzymatic hydrolysis of pretreated wheat straw using cellulase. Based on the resulting glucose concentration the ethanol yield and the residual sugar available for methane production were calculated. The theoretical maximum ethanol yield of wheat straw was estimated to be 0.249 kg kg(-1) dry matter. The achievable maximum ethanol yield per kg wheat straw dry matter pretreated by steam explosion and enzymatic hydrolysis was estimated to be 0.200 kg under pretreatment conditions of 200 degrees C and 10 min corresponding to 80% of the theoretical maximum. The residual methane yield from straw stillage was estimated to be 183 l(N)kg(-1) wheat straw dry matter. Based on the presented experimental data, a concept is proposed that processes wheat straw for ethanol and methane production. The concept of an energy supply system that provides more than two forms of energy is met by (1) upgrading obtained ethanol to fuel-grade quality and providing methane to CHP plants for the production of (2) electric energy and (3) utility steam that in turn can be used to operate distillation columns in the ethanol production process.

Abstract In this work a complex process for production of bioethanol, biomethane, heat and power from the wheat straw is introduced and analyzed with regard to pinch and exergy analysis. The pinch analysis is focused on the bioethanol production where a well-designed heat exchanger network increases heat integration up to 45 MW. To obtain optimal total site external hot and cold utilities demands at different temperature levels as well as maximum power generated by steam turbine, an integrated steam cycle composite curve has been added to the grand composite curve of the “background process”. The exergy analysis takes into account three production sections separately and exergy efficiencies are calculated to find the quantity of irreversibilities the bioethanol processes. The results from exergy analysis show that the bioethanol process has the highest exergy efficiency because of usage of stillage for other processes in which a considerable part of exergy entering is converted into irreversibility because of heat losses and non reacting unknown material produced as material losses.

Abstract Exergy analysis was applied to a novel process for biological production of hydrogen from biomass employing thermophilic and photo-heterotrophic bacteria. The exergy content of the process streams is calculated using a MS-Excel spreadsheet. The scrutinized process incurs an exergy loss of 7–9% of the total exergy input. The efficiency based on chemical exergy of biomass feed and produced pure hydrogen refers to 36–45% depending on the configuration of the overall process. The results presented in the paper underline the strong dependence of obtained exergetic efficiency from definition of products and shows options for process improvement and optimization.

This document describes a PhD proposal framed in a doctoral college entitled “PhD program TU Wien bioactive - Technologies for Drug Discovery and Production”. This project focuses on two main core thematic units: discovery of novel bioactive substances and sustainable production of pharmaceuticals. The first thematic unit focuses on discovering new bioactive substances with pharmaceutical application potential from fungi and plants. The second thematic focuses on the development of a sustainable production process for pharmaceuticals. The present PhD proposal is embedded in this second thematic unit. The presented PhD project is entitled: “Bioactive compounds as main economic drivers for sustainable biorefineries”. The main goal is to use a renewable plant biomass as nutrient source for the bioprocesses of the fungal expression hosts and set up a sustainable biorefinery for maximal resource utilization of the remaining components of the plant biomass. All activities are planned to fulfill requirements of the General Agreement of the project and are subjected to scientific and dissemination activities. Scientific requirements of the project are based on five publications, three of which must be accepted and two must be submitted. Three of these publications must be as first-author and only one can be a non-original publication (review paper). In addition, 14 ECTS have to be fulfilled as part of the doctoral college with specific lectures opened by the coordinators of the college. The project duration is 36 months starting on February 1, 2019 and finishing on January 31, 2022.

Abstract In this paper, a process for the fermentative production of hydrogen is analysed with respect to its exergy efficiency. Parametric studies show the influence of used feedstock, applied process parameters as well as process and heat integration measures on exergy efficiency. It is shown that heat integration and recirculation of fermentor effluents reduce process irreversibilites and the amount of exergy leaving the process in waste streams. Nevertheless, depending on the used feedstock, a large amount of exergy leaves the process via by-products. Internal use of by-products and waste materials for providing process heat could increase chemical exergy efficiency up to 74%.